Do you still need that route?
The BGP advertisement is configured on the customer edge routers using the network command. Route advertisement is conditioned by the appearance of a corresponding network or subnet in the routing table of the edge router. If the network or subnet is manually entered into the routing table by configuring a static route to null 0, the condition is always true because the static route is always there, and the BGP advertisement is always performed.
If the customer edge router loses connectivity to the rest of the customer network but is still connected to the ISP network, BGP advertisement must cease. In this case, BGP advertisement can be stopped if BGP advertisements are bound to the reachability status of a specific subnet in the core of the customer network, according to the customer IGP. The problem with using a static route to null 0 is that it conditions the network statement in the BGP configuration so that BGP always advertises the route. If the customer edge router loses connectivity with the rest of the customer network, the router continues to advertise the entire customer address space. The ISP network receives a valid route from the customer edge router. Traffic is sent to this router, but because the router has lost connectivity with the rest of the network, the traffic is dropped (routed to the null 0 interface using the static route).
Rack1R1#show ip route eigrp 2.0.0.0/24 is subnetted, 1 subnets D 2.2.2.0 [90/2809856] via 192.168.13.3, 00:00:39, Serial1/1 3.0.0.0/24 is subnetted, 1 subnets D 3.3.3.0 [90/2297856] via 192.168.13.3, 00:00:41, Serial1/1 D 192.168.23.0/24 [90/2681856] via 192.168.13.3, 00:00:40, Serial1/1</pre>
Rack1R1#conf te Enter configuration commands, one per line. End with CNTL/Z. Rack1R1(config)#router bgp 12 Rack1R1(config-router)#neigh 2.2.2.2 remote-as 12 Rack1R1(config-router)#neigh 2.2.2.2 up lo0 Rack1R1(config-router)# Rack1R1(config-router)#do show ip bgp summ BGP router identifier 1.1.1.1, local AS number 12 BGP table version is 1, main routing table version 1 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 2.2.2.2 4 12 0 0 0 0 0 never Active Rack1R1(config-router)#exit %BGP-5-ADJCHANGE: neighbor 2.2.2.2; Up
Rack1R1(config)#do show ip route 2.2.2.2 Routing entry for 2.2.2.0/24 Known via "eigrp 100", distance 90, metric 2809856, type internal Redistributing via eigrp 100 Last update from 192.168.13.3 on Serial1/1, 00:01:44 ago Routing Descriptor Blocks: * 192.168.13.3, from 192.168.13.3, 00:01:44 ago, via Serial1/1 Route metric is 2809856, traffic share count is 1 Total delay is 45000 microseconds, minimum bandwidth is 1544 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 2 Rack1R1(config)#do show ip route 3.3.3.3 Routing entry for 3.3.3.0/24 Known via "eigrp 100", distance 90, metric 2297856, type internal Redistributing via eigrp 100 Last update from 192.168.13.3 on Serial1/1, 00:02:09 ago Routing Descriptor Blocks: * 192.168.13.3, from 192.168.13.3, 00:02:09 ago, via Serial1/1 Route metric is 2297856, traffic share count is 1 Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 Rack1R1(config)#ip route 100.10.10.1 255.255.255.255 3.3.3.3 Rack1R1(config)#do show ip route 100.10.10.1 Routing entry for 100.10.10.1/32 Known via "static", distance 1, metric 0 Routing Descriptor Blocks: * 3.3.3.3 Route metric is 0, traffic share count is 1 Rack1R1(config)#ip route 100.20.10.1 255.255.255.255 null0 Rack1R1(config)#do show ip route stat 100.0.0.0/32 is subnetted, 2 subnets S 100.10.10.1 [1/0] via 3.3.3.3 S 100.20.10.1 is directly connected, Null0 Rack1R1(config)#do deb ip routing IP routing debugging is on
Rack1R1(config)#router bgp 12 Rack1R1(config-router)#red static Rack1R1(config-router)#do show ip bgp BGP table version is 3, local router ID is 1.1.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *100.10.10.1/32 0.0.0.0 0 32768 ? *100.20.10.1/32 0.0.0.0 0 32768 ?
Lets Shut down the lo0
RT: delete route to 3.3.3.0 via 192.168.13.3, eigrp metric [90/2297856] RT: SET_LAST_RDB for 3.3.3.0/24 OLD rdb: via 192.168.13.3, Serial1/1 RT: no routes to 3.3.3.0 RT: NET-RED 3.3.3.0/24 RT: delete subnet route to 3.3.3.0/24 RT: NET-RED 3.3.3.0/24 RT: delete network route to 3.0.0.0 RT: NET-RED 3.0.0.0/8
Rack1R1(config-router)#do show ip bgp BGP table version is 3, local router ID is 1.1.1.1 Status codes: s suppressed, d damped, h history, * valid, ; best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *100.10.10.1/32 0.0.0.0 0 32768 ? *100.20.10.1/32 0.0.0.0 0 32768 ? Rack1R1(config-router)#bgp scan-time 5 Rack1R1(config-router)#do show ip bgp BGP table version is 3, local router ID is 1.1.1.1 Status codes: s suppressed, d damped, h history, * valid, ; best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *100.10.10.1/32 0.0.0.0 0 32768 ? *100.20.10.1/32 0.0.0.0 0 32768 ? Rack1R1(config-router)#do show ip bgp BGP table version is 3, local router ID is 1.1.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path 100.10.10.1/32 0.0.0.0 0 32768 ? 100.20.10.1/32 0.0.0.0 0 32768 ? Rack1R1(config-router)#do show ip route sta 100.0.0.0/32 is subnetted, 1 subnets S 100.20.10.1 is directly connected, Null0 Rack1R1(config-router)# RT: del 100.10.10.1/32 via 3.3.3.3, static metric [1/0] RT: delete subnet route to 100.10.10.1/32 RT: NET-RED 100.10.10.1/32 Rack1R1(config-router)#do show ip bgp BGP table version is 4, local router ID is 1.1.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path * 100.20.10.1/32 0.0.0.0 0 32768 ?
So the static route to the null 0 will always be up and advertised via BGP
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